Human Defence Systems Against Disease — AQA GCSE Biology
The body has non-specific barriers to keep pathogens out, and white blood cells to destroy any that get in.
Non-specific defences (keeping pathogens out)
- Skin — a physical barrier; also produces antimicrobial secretions and scabs over wounds.
- Nose — hairs and mucus trap particles and pathogens.
- Trachea and bronchi — lined with mucus (traps pathogens) and cilia (waft mucus up away from the lungs).
- Stomach — produces hydrochloric acid that kills pathogens in food and drink.
White blood cells (destroying pathogens inside)
If pathogens enter the body, white blood cells defend it in three ways:
- Phagocytosis — a white blood cell engulfs and digests the pathogen.
- Antibody production — lymphocytes produce antibodies that are specific to the antigens on a pathogen, marking it for destruction and clumping pathogens together.
- Antitoxin production — antibodies that neutralise toxins released by bacteria.
Why antibodies are specific
Each pathogen has unique antigens (markers) on its surface. A specific antibody fits a specific antigen, like a lock and key.
Exam tips
- Learn the non-specific barriers (skin, nose, trachea/bronchi, stomach acid) and how each works.
- Describe the three white blood cell actions: phagocytosis, antibodies, antitoxins.
- Stress that antibodies are specific to a pathogen's antigens.
- Cilia and mucus work together in the airways.